This invention is directed to air filters and, more particularly, to ram air filters for light aircraft.
The majority of light aircraft, such as the Cessna 150, 172, 182, etc., are driven by internal combustion engines, which include carburetors that control the air/fuel mixture received by the engine. Air entering the carburetor is filtered by a ram air filter, which removes dust and other undesirable particles so as to prevent their entry into the engine via the carburetor.
The most common types of ram air filter presently in use include a metallic housing having relatively large apertures formed in opposing faces. In one type the apertures are enclosed by metal grids between which lie a fluid pervious paper filter. The paper filter is corrugated in a manner such that a plurality of V-shaped pleats are formed. An adhesive positioned along the entire outer length of each of the folds forms a protective cap therefore. The adhesive also attaches the grids to the folds of the paper filter. A pleated filter of this nature is more completely described in U.S. Pat. No. 3,216,578 entitled "Pleated Filter" and issued to T. E. Wright et al. on Nov. 9, 1965. In an alternate type of prior art ram air filter, the metallic housing supports a filter medium formed of pleated screened wire coated with nylon flocking. Usually two pleated layers are included, mounted orthogonally to one another.
Ram air filters of the types described above have a variety of disadvantages. The pleated paper filter types tend to absorb moisture and open up. Obviously, a filter medium with relatively large openings allows relatively large particles to pass and, thus, enter the engine. In addition, moisture loosens the glue attaching the paper filter to its associated support grid. With regard to the pleated screen wire filters, their flocking wears off. As the flocking wears off, relatively large openings are formed. Moreover, in some instances the screen breaks down in a manner such that small bits are drawn into the engine through the carburetor.
Filters of the types described in the foregoing paragraph also have other disadvantages. Because of the manner in which they are formed, the entire structure, including the metallic housing, not just the pleated filter portion, must be replaced, when the filter becomes unusable. Further, because much of the overall filter structure is formed of metal, and because aircraft are often parked where they are exposed to the elements, prior art filters of the type described above often rust. Because they rust, in some instances they must be replaced even though the filtering medium has not reached the point where it is unusable. In addition, it has been found that it is difficult to visually determine when filters of the type described above have deteriorated to the point where they are unusable. Thus, for safety reasons, filters are usually replaced more frequently than absolutely necessary.
It will be appreciated from the foregoing discussion that ram air filters for light aircraft must be frequently replaced. However, replacement prior to the present invention has been more expensive than desirable because, as noted above, the entire filter structure, including the housing must be replaced due to the manner of construction of prior art filters.
Therefore, it is an object of this invention to provide a new and improved air filter for light aircraft.
It is a further object of this invention, to provide a new and improved ram air filter for light aircraft driven by internal combustion engines that is formed substantially entirely of materials that will not rust.
It is a further object of this invention to provide a new and improved ram air filter for light aircraft that includes a reusable housing and a replaceable filter element formed of relatively inexpensive materials.
It is a still further object of this invention to provide a replaceable filter element adapted to be housed in a ram air filter housing that is suitable for use by light aircraft.
It is a still further object of this invention to provide a new and improved replaceable ram air filter element suitable for use by light aircraft that is inexpensive to manufacture and, thus, inexpensive to replace at frequent intervals.